Bleed alleviation in ink-jet inks

ABSTRACT

Color bleed (the invasion of one color into another on the surface of the print medium) using ink-jet inks is alleviated by employing zwitterionic surfactants (ph-sensitive or pH-insensitive) or ionic or non-ionic amphiphiles. The inks of the invention comprise a vehicle and a dye. The vehicle typically comprises a low viscosity, high boiling point solvent, one or two amphiphiles at concentrations above their critical micelle concentration (cmc), while the dye typically comprises any of the dyes commonly employed in ink-jet printing. The amount of surfactant/amphiphile is described in terms of its critical micelle concentration (cmc), which is a unique value for each amphilphile. Above the cmc, micelles form, which attract the dye molecule and thus control the color bleed. Below the cmc, there is no micelle formation, and thus no control of the color bleed.

TECHNICAL FIELD

The present invention relates to inks employed in ink-jet printing,especially in thermal ink-jet printing, and, more particularly, tocolored ink compositions in which color bleed is substantially reducedor even eliminated.

BACKGROUND ART

Heavy dye loads on bond paper of various colored inks can lead to bleedand reduction of waterfastness. Bleed, as used herein, is the invasionof one color into another color on paper, which is a surface phenomenon.This is in contradistinction to uses of the term in the prior art, whichtend to define "bleed" in the context of ink of a single color followingthe fibers of the paper; this is a sub-surface phenomenon.

Surfactants have been used as anti-clogging agents in Japanese Laid-OpenPatent Application No. 63-165465 for use in ink-jet recording inks. Thesurfactants used in that application are limited to those having asurface tension between 20 and 50 dyne/cm. The amount of surfactantranges from about 0.5 to 25 wt%. Specific examples disclosed includesodium dodecyl benzene sulfonate, sodium laurate, and polyethyleneglycol monooleyl ether.

Japanese Laid-Open Patent Application No. 01-203,483 is directed toink-jet recording compositions. Bleed reduction is mentioned inconnection with printing using the inks. However, the compositionsrequire pectin (0.01 to 2 wt%), which is probably being used as athickener. However, pectin is not useful in inks used in thermal ink-jetprinters, due to its thermal instability (it gels at highertemperatures).

Japanese Patent JO 1215-875-A is directed to inks suitable for ink-jetprinting, evidencing good recording with fast drying without bleeding.The compositions all require triglycerides. Such compounds, however, arenot stable to extended shelf life necessary for commercial inks.

Japanese Patent JO 1230-685-A is directed to inks suitable for ink-jetprinting, evidencing quick absorption on the surface of conventionaloffice paper without smear or blotting. The compositions comprisecolorants and liquid solvents and/or dispersants and are characterizedby the presence of a copolymer of ethylene oxide and propylene oxide ofthe formula HO(C₂ H₄ O)_(a--C) ₃ H₆ O(C₂ H₄ O)_(b) H, where a+b is up to50 and b is optionally 0. These copolymers are referred to as"PLURONICS". For the most part, they have not been found to stop bleed.

Thermal ink-jet printers offer a low cost, high quality, andcomparatively noise-free option to other types of printers commonly usedwith computers. Such printers employ a resistor element in a chamberprovided with an egress for ink to enter from a plenum. The plenum isconnected to a reservoir for storing the ink. A plurality of suchresistor elements are arranged in a particular pattern, called aprimitive, in a printhead. Each resistor element is associated with anozzle in a nozzle plate, through which ink is expelled toward a printmedium. The entire assembly of printhead and reservoir comprise anink-jet pen.

In operation, each resistor element is connected via a conductive traceto microprocessor, where current-carrying signals cause one or moreselected elements to heat up. The heating creates a bubble of ink in thechamber, which is expelled through the nozzle toward the print medium.In this way, firing of a plurality of such resistor elements in aparticular order in a given primitive forms alphanumeric characters,performs area-fill, and provides other print capabilities on the medium.

Many inks that are described for use in ink-jet printing are usuallyassociated with non-thermal ink-jet printing. An example of suchnon-thermal ink-jet printing is piezoelectric ink-jet printing, whichemploys a piezoelectric element to expel droplets of ink to the medium.Inks suitably employed in such non-thermal applications often cannot beused in thermal ink-jet printing, due to the effect of heating on theink composition.

A need remains for ink compositions for use in ink-jet printing,particularly thermal ink-jet printing, which do not evidence bleed, asdefined herein, and yet which possess relatively long shelf life andother desirable properties of such inks.

DISCLOSURE OF INVENTION

In accordance with the invention, color bleed on paper media printed byink-jet is alleviated by employing nonionic, pH-sensitive or insensitivezwitterionic (amphoteric) surfactants, or ionic surfactants (amphiphilesor detergents). The ink comprises (a) 0 to about 20 wt% of one or morelow vapor pressure solvents (b) one or more water-soluble dyes, (c) oneor more self-aggregating or performed micellar, vesicular-likecomponents (particular examples and concentrations to be specifiedbelow), and (d) a filler such as water and a biocide, fungicide, and/orslimicide. As used herein, the term "low vapor pressure solvent" refersto a solvent having a vapor pressure that is lower than that of waterand the term "water-soluble dye" refers to a dye whose solubility inwater exceeds 2 wt%.

Low vapor pressure solvents can include, but are not restricted to,glycols such as ethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, propylene glycol, polyethylene glycol,polypropylene glycol, and derivatives thereof; diols such as butanediol,pentanediol, hexanediol, and homologous diols; glycol esters such aspropylene glycol laurate; mono and di glycol ethers such as cellosolves,including ethylene glycol monobutyl ether, diethylene glycol ethers suchas the carbitols, diethylene glycol mono ethyl, butyl, hexyl ethers,propylene glycol ether, dipropylene glycol ether, and triethylene glycolether; long chain alcohols such as butyl alcohol, pentyl alcohol, andhomologous alcohols; and other solvents such as sulfolane, esters,ketones, lactones such as γ-butyro-lactone, lactams such asN-pyrrolidone and N-(2-hydroxyethyl)pyrrolidone, and glycerols and theirderivatives.

Microbial reagents include, but are not limited to, NUOSEPT (Nudex,Inc., a division of Huls Americal, UCARCIDE (Union Carbide), VANCIDE (RTVanderbilt Co.), and PROXEL (ICI Americas).

Dyes include, but are not limited to, anionic water-soluble types suchas C.I. Acid Blue 9 (#42090), C.I. Acid Red 18 (#18), C.I. Acid Red 27(#16185), C.I. Acid Red 52 (#45100), C.I. Acid Yellow 23 (#19140), C.I.Direct Blue 199 (#74190), C.I. Direct Yellow (#29325) and theirmonovalent alkali earth ions such as Na³⁰ , Li³⁰ , Cs³⁰ , NH₄ ⁺, andsubstituted ammonium salts. The dye(s) is present from about 0.1 to 10wt% of the ink.

It is important to note that some ingredients have dual functions. Forexample, n-butyl carbitol can function as a low vapor pressure solventand as a self-aggregating component. Further discussion concerning thecritical role of aggregation and concentration of surfactants inalleviating bleed is provided below. It is sufficient to state here thatcritical concentrations of surfactant are necessary to efficiently andcompletely prevent bleed in double dot mode printing used to generatethe print samples herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows bleed reference patterns where higher bleed indices reflectunacceptable bleed (a bleed score of <2.5 is considered to be acceptablefor high quality text output);

FIG. 2, on coordinates of text print quality (left abscissa) or bleed(right abscissa) and surfactant concentration, shows the qualitativeeffect on print quality and bleed as a function of concentration of asurfactant; and

FIGS. 3a-b, on coordinates of dye concentration and total detergent(surfactant) concentration ([D]_(T)), are plots of dye adsorption tomicelles, with FIG. 3a showing the effect of weak adsorption of dye tomicelle and with FIG. 3b showing the effect of strong adsorption of dyeto micelle, where [D]_(M) is the detergent (surfactant) concentration inmicelles and [D]_(W) is the detergent (surfactant) concentration inwater.

BEST MODES FOR CARRYING OUT THE INVENTION

In the practice of the invention, color bleed resulting from the use ofink-jet inks in thermal ink-jet printers is alleviated by employingeither zwitterionic surfactants or non-ionic amphiphiles. Thezwitterionic surfactants employed in the practice of the invention maybe pH-sensitive or pH-insensitive.

All concentrations herein are in weight percent, unless otherwiseindicated. The purity of all components is that employed in normalcommercial practice for thermal ink-jet inks.

For convenience, examples of bleed alleviating surfactants are dividedinto two categories: (1) non-ionic and amphoteric and (2) ionic. Theformer class is further subdivided into three classes: (a) water-solubleamphiphile mimetics, such as STARBURST dendrimers, which are branchedpolyethylene amines available from Polysciences, Inc., and the like, (b)polyethers, such as ethylene glycol n-butyl ether, diethylene glycoln-butyl ether, diethylene glycol n-hexyl ether, triethylene glycoln-butyl ether, propylene glycol isobutyl ether, the TRITONS, which arenonyl phenyl polyethylene oxide surfactants available from Rohm & HaasCo., the PLURONICS and PLURAFACS, which are polyethylene oxide andpolypropylene oxide block copolymers available from BASF, and theSURFYNOLS, which are acetylenic polyethylene oxide surfactants availablefrom Air Products & Chemicals, Inc., and (c) amphoteric molecules, suchas NDAO, NTAO, NHAO, OOAO, NOAO, and SB3-16; further informationrelating to these compounds is presented below. The ionic class, whichcomprises both cationic and anionic surfactants, also is represented bybile salts (sodium, lithium, ammonium, or substituted-ammonium cholate)and water-soluble dyes.

An example of a pH-sensitive zwitterionic surfactant isN,N-dimethyl-N-dodecyl amine oxide (NDAO), which has a pk_(a) in waterof about 2.3: ##STR1## This compound has a molecular weight of 229, anda critical micelle concentration (cmc; to be discussed in greater detailbelow) of 13 mM.

Also, in place of the C₁₂ H₂₅ - moiety, any R moiety may be used. Thefollowing moieties, their name, abbreviation, molecular weight (mw), andcmc are useful in the practice of the invention:

N,N-dimethyl-N-tetradecyl amine oxide (NTAO); mw =257; cmc =6-8 mM;

N,N-dimethyl-N-hexadecyl amine oxide (NHAO); mw =285; cmc =0.8 mM;

N,N-dimethyl-N-octadecyl amine oxide (NOAO); mw =313; cmc =small;

N,N-dimethyl-N-(Z-9-octadecenyl)-N-amine oxide (OOAO); mw =311; cmc=small.

Another example is N-dodecyl-N,N-dimethyl glycine, which has a pk_(a) ofabout 5 in water: ##STR2##

Yet other examples include phosphates, phosphites, phosphonates,lecithins or the like, and phosphate esters such as phosgomyelin whichhas a pk_(a) of about 2 to 3 in ##STR3## Other similar compounds includephosphoglycerides, such asphosphatidylethanolamines,phosphatidylcholines,phosphatidyl serines,phosphatidylinositols, and B'-O-lysylphosphatidylglycerols.

Additional examples of compounds that are useful in the practice of theinvention include the sulfobetaines, which are zwitterionic, butpH-insensitive: ##STR4## Where n=11, the compound is denoted SB3-12;where n=15, the compound is denoted SB3-16.

Examples of ionic surfactants that are suitably employed in the practiceof the invention include such cationic compounds as ##STR5## cetyltrimethylammonium bromide (CTABr), and such anionic surfactants as CH₃-(CH₂)₁₁ -O-SO₃ -Na^(+sodium) dodecyl sulfate (SDS)

CH₃ -(CH₂)_(n) -SO₃ ⁻ NA+sodium sulfonates

Examples of non-ionic, non-amphoteric surfactants useful in the practiceof the invention include compounds available under the tradenamesTERGITOL, which are alkyl polyethylene oxides available from UnionCarbide, and BRIJ, which are also alkyl polyethylene oxides availablefrom ICI Americas, having the formula:

    CH.sub.3 --(CH.sub.2)--(--O--CH.sub.2 --CH.sub.2 --).sub.m --OH

(where n=3 and m=2, this is n-butyl carbitol, a cellusolve).

Also included in this category are the PLURONICS and the PLURAFACS(BASF) having the general formula:

    HO--(--CH.sub.2 --CH.sub.2 --O--).sub.n --(--CH.sub.2 --CH(CH.sub.3).sub.m --CH.sub.2 --CH.sub.2 --OH

The TRITONS (Rohm & Haas Co.) are generally represented as:

    R--Ph--O(CH.sub.2 --CH.sub.2 --O).sub.y R'

where R, R' is any alkane, alkene, aryl or alkynyl group or H, Ph isphenyl, y=1 to 50, and R is para to the ether linkage on the benzenering.

The SURFYNOLS (Air Products & Chemicals, Inc.) are represented as##STR6## where n+m=0 to 50.

EXAMPLES OF BLEED ALLEVIATING AMPHIPHILES

Zwitterionic surfactants, such as NDAO, NTAO, OOAO, and NOAO, were triedfirst. These surfactants (except for NOAO) are totally miscible inaqueous solutions (about 0.1 to 20 wt%) of diethylene glycol, glycerol,and ethylene and propylene glycol. NOAO is also miscible if up to about10 wt% of a straight chain primary alcohol, such as n-propanol,n-butanol, n-pentanol, is added.

Four examples are included in Table I. NDAO concentrations at 0, 0.5%,1.0%, and 5% surfactant in water was the vehicle. The colors weresimultaneously printed side by side using a dot-on-dot (double pass)algorithm. The dyes used were 1.33% C.I. Acid Red 27 (#16185); 1.65%C.I. Acid Blue 9 (#42090); 1.33% C.I. Direct Yellow 86 (#29325). Table 1shows that without NDAO, massive proliferation of the colors occurs(bleed). NDAO at 0.5% radically alters the extent of bleed, but it isnot eliminated. Table I also shows the effect of increased NDAOconcentrations of 1% and 5%, respectively, concentrations whichsubstantially eliminate bleed. Vehicles which contained 0 to 20% ofdi-ethylene glycol, propylene glycol, or glycerol or 0 to 15%1,5-pentanediol gave similar results with NDAO at approximately the sameconcentrations (see Table III below, Ink #1). NOAO and OOAO required 0to about 10% of a co-solvent, such as 1-propanol, 1-butanol, or1-pentanol, for solubility purposes (see Table III below, Inks #6-11,13-16, 25-27, 29, 30, 31, 33).

The color bleed index values listed in Table I are derived from thescale provided in FIG. 1, which is a print of lines of red (magenta) inkon a background of yellow ink. For high text quality output, a value of≦2.5 is considered to be acceptable. For somewhat lower quality demands,such as printing on boxes, plotting, and the like, a value of about 3 to4 may be considered to be acceptable. Inks commonly used commerciallypresently have values, typically, of about 6 or more.

                  TABLE 1                                                         ______________________________________                                        Bleed Indices for Various Systems.                                            System.sup.1         Wt %.sup.2 Index.sup.3                                   ______________________________________                                        NDAO                 0          6.0+                                                               0.5        4.0                                                                1.0        2.5                                                                5.0        1.0                                           n-pentanol; 1-5-pentanediol                                                                        2.0; 6.0   6.0                                           n-pentanol; 1,5-pentanediol; NDEC.sup.4                                                            2.0; 6.0; 2.0                                                                            2.0                                           CTABr                2.0        3.5                                           DEG; CTABr           6.0; 2.0   2.5                                           SDS                  2.0        3.5                                           n-butanol; 1,4-butanediol; SB3-16                                                                  2.0; 5.0; 8.0                                                                            4.0                                           DEG; PLURONIC L-63   5.0; 5.0   2.5                                           1,5-pentanediol; SURFYNOL S465                                                                     10.0;.2.0  5.0                                           1,5-pentanediol; SURFYNOL S465                                                                     10.0; 4.0  2.0                                           TRITON CF-21         0.7        6.0+                                                               1.0        3.0                                                                3.0        2.0                                           DEG                  5.5        6.0                                           n-butanol            7.0        5.0                                           ______________________________________                                         Notes:                                                                        .sup.1 Dyes include AR27, 1.33%; DY86Na, 1.33%; AB9Na, 1.65%.                 .sup.2 wt %, balance is water.                                                .sup.3 Color Bleed Index; a value of ≦2.5 is considered acceptable     for high quality text output.                                                 .sup.4 N,Ndimethyl-N-dodecyl-N-(ethyl carboxylate).                      

Also shown in Table I is an example in which the vehicle consisted of 2%n-pentanol and 6% 1,5-pentanediol or of 7% n-butanol. The use of suchpaper wetting and penetrating solvents in the inks alone does notalleviate bleed.

Table I shows the effect of employing a (betaine) zwitterionicsurfactant (NDEC) in conjunction with a vehicle of 2% n-pentanol and 6%1,5-pentanediol in stopping bleed. The addition of NDEC surfactantmarkedly reduces the extent of bleed, as compared to the vehicle withoutsurfactant.

Not all zwitterionic surfactants are efficient at eliminating bleed. Forexample, a system comprising 2% n-butanol, 5% 1,4-butanediol, and 8%SB3-16 is not efficient as the other examples in alleviating bleed. Onthe other hand, while bleed is still present, it is reduced compared tothat in which the vehicle is 5.5% DEG, where no surfactant was present.

Small amounts of cationic surfactants in ink also eliminate bleed. Adegree of bleed control (3.5) is achieved using 2% cetyltrimethylammonium bromide (CTABr) in water. The addition of co-solventto the vehicle, specifically 6% diethylene glycol with CTABr present at2%, provides even better bleed control (2.5) than afforded with CTABralone.

Anionic surfactants in inks can control bleed as well. For example, 2%sodium dodecylsulfate (SDS) in water as vehicle controls bleed. Althoughthe color bleed index is 3.5, such an ink would be acceptable for, e.g.,plotters.

Only one non-ionic surfactant of the PLURONIC class, L-63, has beenfound to prevent bleed when present in the ink (see Table I).

Table I shows the effect of increasing SURFYNOL 465 concentration oneliminating bleed: 2% SURFYNOL 465 is not effective, but, 4% SURFYNOL465 controls bleed well in ink vehicles containing 10% 1,5-pentanediolsolvent.

Increasing concentrations of TRITON CF-21 detergent shows similareffects (cf. Table I).

These results show that different classes of surfactants exhibitconcentration dependence on efficient bleed alleviation. Concentrationeffects were observed in the case of non-ionic surfactants, such asn-butyl carbitol, n-butyl propasol, and n-hexyl carbitol (not shown).

It is interesting to note common structural features among these bleedalleviating surfactants. All have features common among surfactants:long hydrocarbon (hydrophobic) tails with polar (hydrophilic)headgroups. Other such detergents of similar structures can beformulated in inks to solve bleed, provided they have structuralfeatures common to these. This does not imply that the bleed alleviatingbehavior is indigenous to all detergents.

The detection of the cmc or the onset of micellization in an ink can bedetermined by a number of methods. Typically, sharp changes are seen inplots of surface tension vs. surfactant concentration (in the ink) orosmotic pressure vs. surfactant concentration (in the ink). These sharpchanges are attributed to the cmc. Other methods, such as conductivity,turbidity, determination of equivalent conductance are precluded inwater-soluble inks.

Bleed Alleviation --Possible Mechanisms

Reference to FIG. 2 gives a hypothetical concentration of surface-activereagent versus bleed and text print quality scale profiles. Basically,this Figure profiles the bleed and text quality responses observed forall surfactants under investigation. FIG. 2 assumes that other coponentsof the ink vehicle and dye(s) concentrations are fixed and that thesurfactant concentration is the dependent variable. From FIG. 2, uponaddition of a small amount of surfactant, there is little change in thebleed control and sharpness of the text print quality. With furtheradditions of surfactant, degradation of text print quality results withlittle or no improvement (perhaps even a slight degradation in bleedalleviation occurs in some cases) in bleed. A surfactant concentrationis finally achieved where the quality of text begins to improve andbleed is reduced. Further decreases in bleed and improvement of textquality may occur with increasing surfactant concentration in the ink.

The lowest surfactant concentration where bleed alleviation andimprovement of text print quality becomes appreciably effective is foundto be near the critical micelle concentration (cmc) or critical monomerconcentration of most surfactants. (The cmc is the concentration ofsurfactant where simple electrolyte or non-electrolyte chemistry lessensin importance to colloid chemistry. For the simple surfactantspreviously described, this is the concentration of surfactant wheremicelles, or aggregated surfactant molecules, begin to appear.)

Micellization is driven by entropic constraints - the hydrocarbon chainsare driven into the interior of the micelle with the hydrophilic,water-soluble groups driven to the exterior. The resulting domainalfluid provides regions of olefin-rich and water-rich pockets, which cancompartmentalize organic solutes such as dyes, co-surfactants, andco-solvent molecules, depending on their hydrophobicity. In addition,micelles interact and find regions in solution where their positional(potential) energy is minimized. It is conceivable that micellescontaining charged dye molecules behave in a similar fashion.

Inspection of Table II shows that the cmcs listed here nicely coincidewith the onset of bleed alleviation in Table I. The cmcs indicated arefor pure water. The tabulated cmc will differ from those in the inkbecause added salts and hydrophobes perturb micelle structure.

                  TABLE II                                                        ______________________________________                                        CMC Data for Surfactant Print Samples                                                        Mole                                                                          wt.   [cmc].sup.1, M                                                                          cmc.sup.1, wt %                                ______________________________________                                        Class                                                                         Surfactant                                                                    Zwitterionic:                                                                 NDAO             229     0.013     0.3                                        C.sub.13 H.sub.27 N(CH.sub.3).sub.2 (CH.sub.2).sub.2 COO.sup.-                                 285     0.015     0.5                                        SB3-12           335     0.012     0.4                                        Ionic:                                                                        CTABr            364      0.0008   0.03                                       SDS              288     0.008     0.23                                       Non-ionic:                                                                    SURFYNOL 465     634     0.03-0.05 2-3                                        TRITON CF-21     489     0.001     0.05                                       N-42             389     ca 0.001  0.04                                       Butyl carbitol   192     0.2-0.3   4-6                                        ______________________________________                                         Note: .sup.1 cmc in pure water at 25° C.                          

Incorporation of dyes into micelles is the probable method by whichsurfactant-containing inks control bleed. Micelles with dye of one colorshot out of an ink-jet pen will not exchange dye of another color in anadjacent micelle on paper medium, because the rate at which the mobilemedium evaporates or adsorbs into the paper is much faster than thedesorption rate of the dye molecules from the micelles or the rate atwhich dye molecules diffuse through the micellar medium. Bleedalleviation results.

The efficiency of this bleed alleviation depends upon the level ofadsorption of the dyes into the micelles, the number concentration ofmicelles in the ink, and the difusion of dye and micelles on the papersurface. FIGS. 3a and 3b show hypothetically the extent of adsorption ofdye into micelles as a function of surfactant concentration for dyemolecules that strongly adsorb to micelles (FIG. 3b) and for dyemolecules that weakly adsorb (FIG. 3a). It will be noted that in theweakly adsorbing dye, a much higher surfactant concentration isnecessary to bind the same amount of dye than in the case of thestrongly adsorbing dye. Obviously, the propensity for dye to adsorb tomicelles is a function of the structure (hydrophobicity) andinteractions of the dye molecule, the surfactant, co-solvent, andco-surfactant (if any) present.

Thus, surfactant concentration affects bleed control. Higherconcentrations of micelles absorb more dye molecules and slow theirdiffusion rate.

Additionally, certain pH-sensitive zwitterionic surfactants will pick upH⁺ from the paper and change it from a zwitterionic surfactant to acationic one. ##STR7##

This occurs on the paper surface. Anionic dyes such as those mentionedabove complex with this cationic surfactant on the paper surface toproduce a water-insoluble complex of dye and surfactant, such as##STR8##

Because these insoluble complexes do not diffuse, bleed control isachieved.

INDUSTRIAL APPLICABILITY

The ink compositions of the invention are expected to find use inthermal ink-jet inks, especially color inks, where bleed of one colorinto another is a concern. The ink compositions of the invention reduceor even eliminate such color bleed.

EXAMPLES

The following inks were prepared, as listed in Table III, below (thedyes and dye concentrations were as listed above and the balance waswater):

                  TABLE III                                                       ______________________________________                                        Ink Compositions.                                                             Ink # Amp1     Amp2     NaCh.sup.1                                                                           Solvent1                                                                              Solvent2                               ______________________________________                                         1    NDAO                     DEG                                                  1%                       6%                                              2    S465.sup.2               DEG                                                    1.5%                   6%                                              3    S465                     DEG                                                    1.5%                   10%                                             4    NTAO     S465            DEG                                                    1.0%   0.5%            10%                                             5    NDAO     S465            DEG                                                    2.5%   1.0%            10%                                             6    NOAO                     DEG     n-BuOH.sup.3                                 4%                       3%      7%                                      7    OOAO                     DEG     n-BuOH                                       2%                       6%      2%                                      8    NOAO     S465            DEG     n-BuOH                                       4%       0.5%            6%      7%                                      9    OOAO     S465            DEG     n-BuOH                                       2%       0.5%            6%      2%                                     10    NOAO                     DEG     n-BuOH                                       4%                       6%      7%                                     11    OOAO     S465            DEG     n-BuOH                                       2%       0.5%     3.7%   6%      2%                                     12    nBC.sup.4                                                                     6%                                                                      13    NOAO     S465            DEG     n-BuOH                                       4%       1%       0.5%   6%      3%                                     14    NOAO     nBC                     n-BuOH                                       6%       6%       2%             3%                                     15    OOAO     S465            DEG     n-BuOH                                       3%       0.5%     0.5%   6%      3%                                     16    OOAO     S465            DPM.sup.5                                                                             n-BuOH                                       3%       0.5%     0.5%   6%      3%                                     17    NOAO     S465            .sup. 1,4-BD.sup.6                                   6%       0.5%     2%     5%                                             18    NOAO     S465            1,4-BD                                               6%       1%       2%     5%                                             19    OOAO     S465            DEG                                                  6%       0.5%     0.5%     5.7%                                         20    OOAO     S465            DEG                                                  3%       0.5%     0.5%     5.7%                                         21    OOAO     S465     LiCh.sup.7                                                                           DEG                                                  3%       05%      0.5%   6%                                             22    L63.sup.8                                                                     6%                                                                      23    n-BuP.sup.9                                                                   5%                                                                      24    nBC                                                                           8%                                                                      25    OOAO                     1,4-BD  n-BuOH                                       7%                       5%      2%                                     26    NTAO                     1,4-BD  n-BuOH                                       7%                       5%      2%                                      27*  OOAO     S465            .sup. 1,5-PD.sup.10                                                                   n-BuOH                                       3%       0.5%            6%      3%                                     28    nBC      nHC.sup.11                                                           4%       1%                                                              29*  NOAO     NHAO            1,5-PD  peOH.sup.12                                  4%       6%              6%      2%                                     30    NHAO                     1,4-BD  BuOH                                         7%                       5%      2%                                     31    OOAO     S465            1,4-BD  BuOH                                         6%        0.25%    0.25% 5%        1.75%                                32    OOAO     nBC                                                                  3%       8%       2.5%                                                   33*  NOAO     OOAO            1,5-PD  peOH                                         6%       2%              7%      2%                                     ______________________________________                                         Notes:                                                                        .sup.1 sodium cholate                                                         .sup.2 SURFYNOL 465                                                           .sup.3 nbutanol                                                               .sup.4 nbutyl carbitol                                                        .sup.5 DOWANOL DPM (cellosolve of Dow Chemical Co.)                           .sup.6 1,4butanediol                                                          .sup.7 lithium cholate                                                        .sup.8 PLURONIC L63                                                           .sup.9 nbutylpropasol                                                         .sup.10 1,5pentanediol                                                        .sup.11 nhexyl carbitol                                                       .sup.12 npentanol                                                             *These inks have a color bleed index of ≦2.5; the remaining inks       have a color bleed index ranging from about 3 to 4.                      

What is claimed is:
 1. A process for reducing color bleed in inksemployed in thermal ink-jet printing, comprising printing a first ink ona medium followed by substantially simultaneously printing a second inkadjacent thereto, each said ink having the following composition:(a) avehicle; and (b) about 0.1 to 10 wt% of at least one water-solubleanionic dye dissolved therein,wherein said vehicle comprises (1) atleast one member selected from the group consisting of zwitterionicsurfactants and non-ionic amphiphiles, present in an amount that is atleast equal to its critical micelle concentration; (2) 0 to about 20 wt%of at least one organic solvent which supports the micelle formation ofsaid at least one member; and (3) the balance water, whereby invasion ofone color by another is avoided.
 2. The process of claim 1 wherein saidzwitterionic surfactants are selected from the group consisting ofnon-ionic compounds and ionic compounds.
 3. The process of claim 2wherein said non-ionic compounds are selected from the group consistingof water-soluble amphiphile mimetics, polyethers, polyethylene oxides,acetyplenic backboned polyethylene oxides, and amphoteric compounds. 4.The process of claim 3 wherein said mimetics are branched polyethyleneamines.
 5. The process of claim 3 wherein said polyethers are selectedfrom the group consisting of ethylene glycol n-butyl ether, diethyleneglycol n-butyl ether, diethylene glycol n-hexyl ether, triethyleneglycol n-butyl ether, and propylene glycol isobutyl ether.
 6. Theprocess of claim 3 wherein said amphoteric surfactants are pH-sensitivesurfactants selected from the group consisting of N,N-dimethyl-N-dodecylamine oxide, N,N-dimethyl-N-tetradecyl amine oxide,N,N-dimethyl-N-hexadecyl amine oxide, N,N-dimethyl-N-octadecyl amineoxide, N,N-dimethyl-N-(Z-9-octadecenyl)-N-amine oxide,N-dodecyl-N,N-dimethyl glycine, phosphates, phosphites, phosphonates,lecithins, phosphate esters, phospatidylethanolamines,phosphatidylcholines, phosphatidyl serines, phosphatidylinositos, andB'-O-lysylphosphatidylglycerols.
 7. The process of claim 3 wherein saidamphoteric surfactants are pH-insensitive surfactants comprisingsulfobetaines.
 8. The process of claim 2 wherein said ionic surfactantsare selected from the group consisting of cetyl trimethylammoniumbromide, sodium dodecyl sulfate, sodium sulfonates.
 9. The process ofclaim 1 wherein said organic solvent is selected from the groupconsisting of glycols, diols, glycol esters, glycol ethers, long chainalcohols, sulfolane esters, ketones, lactones, and glycerols, andderivatives thereof and mixtures thereof.
 10. The process of claim 9wherein said solvent is selected from the group consisting of ethyleneglycol, diethylene glycol, triethylene glycol, tetraethylene glycol,propylene glycol, polyethylene glycol, polypropylene glycol, andderivatives thereof; butanediol, pentanediol, hexanediol, and homologousdiols; propylene glycol laurate; ethylene glycol monobutyl ether,diethylene glycol mono ethyl ether, diethylene glycol mono butyl ether,diethylene glycol mono hexyl ether, propylene glycol ether, dipropyleneglycol ether, and triethylene glycol ether; butyl alcohol, pentylalcohol, and homologous alcohols; γ-butyrolactone, N-pyrrolidone andN-(2-hydroxyethyl)pyrrolidone, and glycerols and their derivatives. 11.The process of claim 1 wherein said dye is a water-soluble anionic dyeselected from the group consisting of C.I. Acid Blue 9, C.I. Acid Red18, C.I. Acid Red 27, C.I. Acid Red 52, C.I. Acid Yellow 23, C.I. DirectBlue 199, and C.I. Direct Yellow
 86. 12. The process of claim 11 whereinsaid anionic dye is associated with a cation selected from the groupconsisting of monovalent alkali earth ions, NH₄ ⁺, and substitutedammoniun salts.
 13. The process of claim 1 wherein said ink consistsessentially of:about3wt%N,N-dimethyl-N-(Z-9-octadecenyl)-N-amine oxide;about 0.5wt% of an acetylenic polyethylene oxide surfactant; about 6wt%pentanediol; about 3wt% n-butanol; a dye selected from the groupconsisting of 1.33wt% Acid Red 27, about 1.33% Direct Yellow 86, andabout 1.65wt% Acid Blue 9-Na; and the balance water.
 14. The process ofclaim 1 wherein said ink consists essentially of:about 4 wt%N,N-dimethyl-N-octadecyl amine oxide; about 6 wt%N,N-dimethyl-N-hexadecyl amine oxide; about 6 wt% pentanedio; about 2wt% n-pentanol; a dye selected from the group consisting of 1.33wt% AcidRed 27, about 1.33wt% Direct Yellow 86, and about 1.65wt% Acid Blue9-Na; and the balance water.
 15. The process of claim 1 wherein said inkconsists essentially of:about 6wt% N,N-dimethyl-N-octadecyl amine oxide;about2wt% N,N-dimethyl-N-(Z-9-octadecenyl)-N-amine oxide; about 7wt%pentanediol; about 2wt% n-pentanol; a dye selected from the groupconsisting of 1.33wt% Acid Red 27, about 1.33wt% Direct Yellow 86, andabout 1.65wt% Acid Blue 9-Na; and the balance water.
 16. A process forreducing color bleed in inks employed in thermal ink-jet printing,comprising printing a first ink on a medium followed by substantiallysimultaneously printing a second ink adjacent thereto, each said inkhaving the following composition:(a) a vehicle; and (b) 0.1 to about 10wt% of at least one water-soluble anionic dye dissolved therein, whereinsaid vehicle comprises (1) at least one member selected from the groupconsisting of N,N-dimethyl-N-dodecyl amine oxideN,N-dimethyl-N-hexadecyl amine oxide, N,N-dimethyl-N-octadecyl amineoxide, N,N-dimethyl-N-(z-9-octadecenyl)-N-amine oxide, present in anamount that is at least equal to its critical micelle concentratio; (2)0 to about 20 wt% of at least one organic solvent selected from thegroup consisting of pentanediol, pentanol, and butanol; and (3) thebalance water, whereby invasion of one color by another is avoided. 17.the process of claim 16 wherein said dye is a water-soluble anionic dyeselected from the group consisting of C.I. Acid Blue 9, C.I. Acid Red18, C.I. Acid Red 27, C.I. Acid Red 52, C.I. Acid Yellow 23, C.I. DirectBlue 199, and C.I. Direct Yellow
 86. 18. The process of claim 17 whereinsaid anionic dye is associated with a cation selected from the groupconsisting of monovalent alkali earth ions, Nh₄ +, and substitutedammonium salts.